Referring now to FIG. 1, a block diagram of an engine 100 according to the prior art is presented. Air is drawn through a throttle body 102 into an intake manifold 104. A representative cylinder 106 includes an intake valve 108 and an exhaust valve 110. The intake valve 108 allows an air-fuel mixture to be drawn into the cylinder 106. The intake valve 108 is controlled by an intake camshaft 112, while the exhaust valve 110 is controlled by an exhaust camshaft 114. The intake valve 108 opens and closes as the intake camshaft 112 rotates. Likewise, the exhaust valve 110 opens and closes as the exhaust camshaft 114 rotates.
Traditionally, the intake and exhaust camshafts, 112 and 114, have been driven directly by the crankshaft (not shown) via a belt or chain. The rotational position of the camshafts, 112 and 114, determines the times, with respect to crankshaft position that the intake and exhaust valves, 108 and 110, open. At a certain time, an ignition coil 116 provides a high voltage to a spark plug 118 that ignites the air-fuel mixture within the representative cylinder 106. When the exhaust valve 110 opens, combustion products are output to an exhaust system 120.
To give the engine designer more flexibility, cam phasers have been devised. An intake cam phaser 122 can change the rotational position of the intake camshaft 112 with respect to the crankshaft. Likewise, an exhaust cam phaser 124 can change the rotational position of the exhaust camshaft 114 with respect to the crankshaft. When the intake and exhaust cam phasers 122, and 124, are actuated, spark calculations are updated to incorporate the new target position of the cam phasers.